jsonrpc: Return an error if funding amount is too large

Fixes #516

Reported-by: @instagibbs
Signed-off-by: Christian Decker <decker.christian@gmail.com>

lightningd/peer_control.c

@@ -2559,6 +2559,11 @@ static void json_fund_channel(struct command *cmd,
 		return;
 	}
 
+	if (fc->funding_satoshi >= MAX_FUNDING_MSATOSHI) {
+		command_fail(cmd, "Funding msatoshi must be < %d", MAX_FUNDING_MSATOSHI);
+		return;
+	}
+
 	/* FIXME: Support push_msat? */
 	fc->push_msat = 0;
 

lightningd/peer_control.h

@@ -14,6 +14,7 @@
 #include <wire/peer_wire.h>
 
 #define ANNOUNCE_MIN_DEPTH 6
+#define MAX_FUNDING_MSATOSHI (1 << 24)
 
 struct crypto_state;